THE SENSORY BASIS OF READING AND READING PROBLEMS

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THE SENSORY BASIS OF READING AND READING
PROBLEMS Peter C. Hansen, Joel B. Talcott,
Caroline Witton, Catherine J. Stoodley John F.
Stein. University Laboratory of Physiology,
Parks Road, Oxford OX1 3PT, UK.

• Background
• Developmental dyslexia is a specific disorder of
  reading often associated with deficits in
  detecting dynamic auditory and visual stimuli.
• Deficits in detecting visual and auditory
  transients contrasts with normal detection
  thresholds for more static stimuli that are not
  tracked temporally.
• In normally-reading children, auditory and
  visual dynamic sensitivity helps constrain the
  development of childrens phonological and
  orthographic skills respectively both are
  important for skilled reading.

• Dynamic Visual Processing
• Thresholds for detecting coherent motion in
  random dot displays provide a good measure of the
  sensitivity of the visual transient system at a
  cortical level (e.g., V5/MT).
• Coherent form sensitivity provides a good
  control measure for coherent motion. Many cells
  in V4 respond strongly to concentric circle
  stimuli

• General Psychophysical Method
• Thresholds are measured using a standard 2
  interval, 2 alternative forced-choice method
  using standard staircase procedures.
• Long duration stimuli are used to distinguish
  between detection of stimulus rate from rate of
  stimulus detection.
• Catch trials included to monitor attention and
  task compliance.

Audition
1.
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GROUP DIFFERENCES Vision

• Dyslexics significantly less sensitive than the
  controls to 2 Hz FM, 40 Hz FM, but not 240 Hz FM
  and 20 Hz AM.

1.
2.
p gt 0.05
p 0.001

• Two routes can be used to read most words a
  visual strategy at the whole word level (red
  stream) or by decoding the word into constituent
  phonemes (blue stream).
• Both routes are important for the development of
  a skilled reader.
• Most dyslexic readers demonstrate deficits in
  both phonological
• and orthographic reading skills.
• Some dyslexics demonstrate relatively pure
  deficits that are apparently restricted to one
  route.

• Our published work has shown that dyslexics are
  less sensitive than non-reading impaired controls
  to coherent motion

p 0.04
p gt 0.05
2.

• The dyslexics were significantly less sensitive
  than the controls to 2 Hz FM and 20 Hz AM.
• No group differences were found for 2 Hz AM or
  240 Hz FM detection.

Measures of Orthographic and Phonological
Processing

• We and other laboratories have shown in a
  number of studies (see 2., above), the
  consistency of the group difference on motion
  detection tasks.
• Effect size (con mean- dys. mean) /St. Dev.
  (dys, con pooled)

Orthographic Choice
Phonological Choice
Studies of Unselected School Children
Requires use of spelling to sound rules
Requires visual analysis
3.
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Talcott, Witton, McLean et al, 2000

• Coherent Motion sensitivity was a good
  predictor of childrens orthographic skills
• Childrens phonological skills were best
  predicted by sensitivity to FM at 2 Hz.

• No significant group difference has been found
  for the control task of coherent form detection.
• Visual deficits restricted to detection of
  dynamic stimuli?